Semiconductor image sensors are used to sense radiation such as lights. Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) are widely used in various applications such as digital camera or mobile phone camera. These devices utilize an array of pixels located in a substrate, including photodiodes and transistors that can absorb radiation projected toward the substrate, and convert the sensed radiation into electrical signals.
A back side illuminated (BSI) image sensor device is one type of image sensor device. These BSI image sensor devices detect lights projected from the backside of the image sensor devices. A BSI image sensor device has a relatively thin silicon substrate (e.g., a few microns thick) in which light-sensing pixels are formed. The quantum efficiency and the well capacity of the BSI image sensors depend on the size of the radiation-sensing region. Interference between light-sensing pixels becomes problematic when the pixel density increases. Some BSI CIS products use grids to avoid crosstalk between pixels, but still cannot eliminate the crosstalk.